Internal mixer with wide throat and wear plates

ABSTRACT

A wide throat internal mixer and method of mixing a batch of petrochemical material wherein bales are fed by a corresponding large size ram weight from a large size hopper into a mixing chamber through a corresponding large size throat opening having wear plates.

TECHNICAL FIELD

This invention relates to high intensity mixing machines for elastomericmaterials. A batch of ingredients including carbon black is fed into ahopper which has a ram weight connected to a piston rod for controllingmovement of the materials into the mixer. The hopper is closed exceptwhen the ingredients are being loaded.

BACKGROUND ART

Internal mixers of a 8.36 cubic feet (237 liter) size such as a thatshown in U.S. Pat. No. 5,492,403 have been made and operated in rubberplants for many years. The mixer body has had a rectangular throatopening of 11.5 inches (29.21 cm) by 32 inches (81.28 cm), apiston-cylinder with an 11 inch diameter (27.94 cm) for operation on 100psi, (7.03 kg/sq cm), factory supplied air pressure providing aneffective stock pressure of 27.2 psi (1.91 kg/sq cm). Mixing time, thatis the time required to raise the temperature of the rubber mixture fromambient (room temperature) of 80° F.-90° F. (27° C.-32° C.) to adischarge temperature of 350° F., (662° C.) has been 3.5 to fourminutes. Loading time has taken from one to several minutes.

The mixer body has been replaced approximately every seven years becauseof wear in the throat area and inside the mixer body. Completereplacement of these 237 liter mixers with new larger mixers has notbeen feasible in older rubber plants because of the increased weight ofthe new mixers which would require extensive changes to the rubberplant. Also the cost of new mixers and other equipment for the largersize mixer is substantial. [$2,200,000 for a new 8.36 cubic foot (270liter) mixer assembly].

DISCLOSURE OF INVENTION

The present invention is directed to a modification of the present 8.36cubic feet (237 liter) size internal mixer which does not requireenlarging the size of the mixer body. By increasing the size of thethroat of the mixer body, adding a new size ram weight and hopper and anew size piston-cylinder apparatus, substantial improvements inproduction and quality have been achieved. Also, by adding wear platesat the throat area, the time between replacements of the mixer body hasbeen increased.

In accordance with one aspect of the invention there is provided: aninternal mixer for mixing petrochemical materials and other ingredientsto be vulcanized comprising a mixer body, a mixing chamber in the body,a throat opening for charging the mixer, a discharge opening fordischarging the mixer, a ram weight, a hopper and a piston-cylinderassembly for urging the ram weight into the throat opening and applyingpressure to the petrochemical materials and other ingredients in themixing chamber characterized by the mixing chamber having a volume notover 8.36 cubic feet (237 liters), the throat opening having an area ofat least 576 square inches (3,715 cm²), the hopper having a crosssectional area of at least 576 square inches and the ram having an areaof at least 576 square inches (3,715 cm²).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fragmentary sectional view of a prior art internal mixerassembly.

FIG. 2 is a fragmentary sectional view of the internal mixer having thesame size mixer body as the mixer of FIG. 1 and the wide throat andother improvements embodying the present invention.

FIG. 3 is an enlarged fragmentary plan view of the mixer body takenalong line 3—3 in FIG. 2 showing the wide throat and wear plates.

FIG. 4 is a sectional view of the mixer body showing the throat and wearplates taken along line 4—4 in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a prior art internal mixer assembly 10 is shownhaving a mixer body 12 with a mixing chamber 14 having a capacity of8.36 cubic feet (237 liters). A door 16 (shown in the closed condition)is provided to close a discharge opening 18 in the mixer body 12. Athroat 20 is provided in an upper wall 22 of the mixer body forreceiving the ingredients to be mixed from a hopper 24 mounted on theupper wall 22 of the mixer body 12. A piston-cylinder assembly 26 ismounted on the hopper 24 with a piston 28 fastened to a piston rod 30connected to a ram weight 32 located in the hopper 24.

In this prior art internal mixer assembly 10 the throat 20 in the mixerbody 12 has an opening having a width of 11½ inches (29.21 cm) and alength of 32 inches (81.28 cm) or a total area of 368 square inches(2,373.65 sq cm). The ram weight 32 and the hopper 24 are ofsubstantially the same size for movement of the ram weight into thethroat 20 during operation of this internal mixer assembly 10.

The piston-cylinder assembly 26 has an air inlet pipe 34 incommunication with a supply of air pressure from the factory which maybe 100 psi (7.03 kg/sq cm). The diameter of the piston 28 is 11 inches(27.94 cm) and is slidably mounted in a cylinder 36 of thepiston-cylinder assembly 26. The cylinder 36 also has a diameter of 11inches (27.94 cm). A loading door 38 is hinged in the hopper 24 and ismovable to an open position not shown for adding ingredients to thehopper.

With reference to FIG. 2, an internal mixer assembly 40 is shownembodying the invention wherein the mixer body 12′ is the same as themixer body 12 of the prior art internal mixer assembly 10, except a newthroat opening 42 has a width w of 18 inches (45.72 cm) and a length of32 inches (81.28 cm). This provides an area of 576 square inches (3,715sq cm) in contrast to the area of the throat 20 of the prior artassembly 10, which is 368 square inches (2,378.60 sq cm). The new throatopening 42 also has wear plates 44 and 46 covering the side surfaces ofthe opening.

Mounted on the mixer body 12′ is a hopper 48 containing a ram weight 50.The ram weight 50 is sized to fit in the new throat opening 42 and has awidth of 17.625 inches (44.76 cm) and a length of 31.625 inches (80.32cm), providing enough clearance to slide into the new throat opening.Mounted on the hopper 48 is a piston-cylinder assembly 52 having apiston 54 slidably in mounted in a cylinder 56 with a piston rod 58connected to the ram weight 50. A pipe 60 in communication with thecylinder 56 and a source of factory air is also provided at the top ofthe cylinder 56. The piston and cylinder have a diameter of 22 inches(55.88 cm) and the factory supply of air pressure may be around 79 psi(5.55 kg/sq cm). A loading door 62 may be hinged in the side of thehopper 48 and is movable to an open position not shown for addingingredients to the hopper.

The wear plates 44 and 46 of the new throat opening 42 are of a materialsuch as heat tempered steel plate having a 55-60 Rockwell hardness whichis of greater hardness than the cast steel material of the ram weight50. This results in the ram weight 50 wearing out sooner than the wearplates 44 and 46 at the throat 42 of the mixer body 12′. With thisconstruction there is a savings in the replacement of worn parts sinceit is less costly to replace the ram weight 50 than the mixer body 12′.

In operation it has been found that substantial improvements inproduction and quality of the mixing have been achieved with the newinternal mixer assembly 40. In loading the mixer 40, bales ofpetrochemicals, such as natural rubber, are fed into the throat openings20 and 42. These bales have one side of 11.5 inches by 32 inches (29.21cm by 81.28 cm) and it has been found that because of the wider throatopening of the new internal mixer assembly 40 there is an improvement inloading which can be done automatically in 45 seconds for each charge.Other ingredients which are mixed in with the petrochemicals areparaffins, carbon black in powder or granule form and process oils whichmay be heated in liquid form. With the new internal mixer assembly 40 ithas been found that the dispersion of the carbon black and heated oilsin the mixed product over the dispersion in the mixture produced by theprior art mixer assembly 10 is much improved. This has been determinedby examining the product for dispersion under magnification.

The new internal mixer assembly 40 provides mixing under an effectivestock pressure of 54 psi (3.94 kg/sq cm). This is compared with aneffective stock pressure of 27.2 psi (1.91 kg/sq cm) for the prior artinternal mixer assembly 10. Effective stock pressure is the product ofthe pressure in the cylinder 26 and the face area of the piston 54divided by the ram weight 50. The mixing time has also been reduced to1.5 minutes from 3.5 to 4 minutes necessary with the prior art internalmixing assembly 10. The mixing time is determined by the time requiredto increase the temperature from the feeding temperature, or ambient(room) temperature of 80° to 90° Fahrenheit (270 to 32° C.) to adischarge temperature of 350° F. (177° C.). It is believed the rapidincrease in temperature is due to the increased size of the ram weight50 and the pressure exerted by the ram weight on the batch of rubber inthe mixer chamber 14′. After the batch of rubber is mixed, the door 16′is opened to discharge the batch from the mixing chamber 14′. With thenew internal mixer assembly 40 the loading time has been reduced to 45seconds from the 1 to several minutes with the prior art mixer assembly10. This is a substantial savings in a 24 hour period of continuousoperation.

From these test results it has been demonstrated that without anysubstantial change to the mixer body 12 substantial improvements inproduction and quality can be obtained. This has resulted in largesavings in not having to buy new and larger equipment and redesigningfactory space for the larger equipment. Before this invention, largerinternal mixers were designed and made with 9.53 cubic feet (270 liter)volumes, whereas the new internal mixer assembly 40 makes thiseconomically unnecessary at this time.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention. Having thusdescribed the invention, it is now claimed:

We claim:
 1. An internal mixer (46) for mixing petrochemical materialsand other ingredients comprising a mixer body, a mixing chamber (14) insaid body, a throat opening (42) for charging said mixer, a dischargeopening (18′) for discharging said mixer, a ram weight (50), a hopper(48) and a piston-cylinder assembly (52) for urging said ram weight (50)into said throat opening (42) and applying pressure to saidpetrochemical materials and said other ingredients in said mixingchamber (14), said mixing chamber (14) having a volume not over 8.36cubic feet (237 liters), characterized by said throat opening (42)having an area of at least 576 square inches (3.715 sq. cm), said hopper(48) having a cross sectional area of at least 576 square inches (3.715sq. cm), and said ram weight (50) having an area of at least 576 squareinches (3.715 sq. cm).
 2. The internal mixer (40) of claim 1 furthercharacterized by each of said throat opening (42) and said ram weight(50) being about 18 inches (45.72 cm) wide and about 32 inches (81.28cm) long.
 3. The internal mixer (40) of claim 1 further characterized bysaid hopper (48) having a cross section size of at least 18 inches wide(45.72 cm) and 32 inches long (81.28 cm).
 4. The internal mixer (12′) ofclaim 1 further characterized by said piston-cylinder assembly (52)having a piston (54) and cylinder (56) diameter of at least 22 inches(55.88 cm).
 5. The internal mixer (40) of claim 4 further characterizedby said piston-cylinder assembly (52) being in communication with asource of factory air pressure of at least 79 psi (5.55 kg/sq cm)whereby effective stock pressure in said mixing chamber (12′) will be atleast 54 psi (3.94 kg/sq cm).
 6. The internal mixer (40) of claim 1further characterized by said throat opening in said mixing chamberbeing covered with wear plates of a material of greater hardness thanthe material of said ram weight to increase the wear life of said throatopening and said mixing chamber.
 7. A method of mixing a batch ofpetrochemical materials and other ingredients in an internal mixer (40)having a mixing chamber with a volume of 8.36 cubic ft (237 liters), anda mixer body throat opening (42), a discharge opening (18′), a feedhopper (48) mounted on said mixer (40) over said throat opening (42), aram weight (50) in said hopper (48) connected to a piston rod (58) of apiston-cylinder assembly (52) mounted on said hopper (48) comprising: a.feeding said batch of petrochemical materials in the form of bales andsaid other ingredients into said hopper (48) and through said throatopening (42); characterized by: b. moving said ram weight (50) into saidthroat opening (42) with said throat opening (42) having a width of 18inches (45.72 cm) and a length of 32 inches (81.28 cm) to provide aneffective stock pressure of about 54 psi (3.94 kg/sq cm) with a pressurein said piston cylinder assembly (52) of about 79 psi (5.55 kg/sq cm);c. mixing said batch at said effective stock pressure until thetemperature is raised to a predetermined discharge temperature; and d.discharging said batch from said mixing chamber (14′) through saiddischarge opening (18′).
 8. The method of claim 7 further characterizedby bales of petrochemicals having one side smaller than said mixer bodythroat opening (18′).
 9. The method of claim 8 further characterized bysaid one side of said bales being not over 11.5 inches by 32 inches(29.21 cm by 81.28 cm).
 10. The method of claim 8 further characterizedby mixing said batch until the temperature is raised to a dischargetemperature of about 350 degrees F. (177 degrees C.).
 11. The method ofclaim 7 further characterized by said ram weight (50) having an areasubstantially the same as the area of said throat opening (42) toprovide effective stock pressure and accelerate the increase intemperature of said batch during said mixing.